Download Sensa1on and Percep1on

Sensa&onandPercep&on
PSYC111-Lecture5
Dr.J.Nicol
Sensa&onandPercep&on
• Sensa&onistheactofusingoursensoryreceptorsto
detectthepresenceofas&mulusandtotransmitan
electricalsignaltothebrainwithinforma&onaboutit
• Signalissenttothebrainwhereitisfurtherprocessed
andinterpreted,thisprocesswhichalsoinvolves
recogni&onandiden&fica&oniscalledpercep&on
• Thetransforma&onofphysicalenergyfromthe
environmentintoanelectricalsignalinthenervous
systemiscalledtransduc&on
SensorySystems
• Sensoryreceptorsreceives&mulusinforma&onand
conductthatinforma&ontospecificpartsofthebrain
thatareresponsibleforprocessingthatkindofsensory
informa&on
• Eachsystemconsistsof:sensoryreceptors,neural
pathways,andbrainareasthatareinvolvedin
percep&on
• Sensa&onandpercep&onoccurdifferentlyineachof
oursensorymodali&es,butoursensessharesome
commonprocesses
SensoryReceptorCells
Eachofoursenseshasasetofspecializedcellsthat
convertaspecificformofphysicalenergyintoneural
impulses-thisconversioniscalledsensorytransduc&on
SensoryAdapta&on
• Oursensorysystemsaredesignedtodetectchangesin
theenvironment
• HelpsusfocusouraQen&ononlyonwhatisimportant
intheenvironment,byrespondingtothecon&nual
presenceofthesames&mulusortoarepe&&ve
s&muluswithaprogressivelyweakerresponse
• Adap&vebecauseitkeepsthebrainfrombeing
overloadedwithredundantincominginforma&on
• Canbeovercomebyexposuretoamuchstronger
s&mulus
SensoryThresholds
• Sensoryreceptorshavedetec&onthresholds-theydo
notdetectallthes&mulithatareintheenvironment,
onlythosethatareofaminimumlevelofintensity
• Thresholdslimitourabili&es,buttheyareadap&ve
becausetheypreventusfrombeingdistractedbysmall
andunimportantchangesintheenvironment
• Psychophysics:afieldthatexaminestherela&onship
betweenthephysicalcharacteris&csofas&mulusand
thepsychologicalpercep&onofthats&mulus
SensoryThresholds
• Absolutethreshold:theminimumamountofs&mulus
energythatisnecessaryforsensorydetec&on
• Differencethreshold:thesmallestdifferencebetween
twos&mulithatcanbedetected(i.e.,JND)
• Signaldetec&ontheory:ourabilitytodetects&muli
thatarepresentedatnearthresholdlevelsis
determinedbytwoprocesses:
• Sensorysensi&vity(i.e.,asensoryprocess)
• Responsebias(i.e.,adecisionprocess)
Goodperformanceinadetec&ontaskrequirestheabilityto
accuratelyreportwhenatargetispresentANDwhenitisnot
PerceptualProcessing
• Percep&oninvolvesbothsimultaneousboQom-upand
top-downprocessing
• BoQom-upprocessing:transduc&onofenvironmental
s&muliintoneuralimpulsesthatproceedintomore
complexbrainregions(i.e.,froms&mulusup)
• Top-downprocessing:ledbycogni&veprocessessuch
asmemory,knowledge,andperceptualexpecta&ons
Sensa&onWithoutPercep&on
• Experienceislimitedtotheenergythatcanabsorbed
bysensoryreceptorsandconvertedtoneuralimpulses
transmiQedtothebrain(Goldstein,2014)
• Ateverywakingmomentthereismoreinforma&on
impingingonoursensorysystemsthanwecanprocess
• Muchofwhattakesplacearoundusgoesundetected
byourperceptualsystems!(Simons&Chabris,1999)
Chabrisetal.(2011)
Greenwaldetal.(1991)
Greenwaldetal.(1991)
Merikle&Skanes(1992)
Strahanetal.(2002)
Zajonc(1980)
deGrootetal.(2012)
deGrootetal.(2012)
VisualSensa&on
• Electromagne&cradia&onproduceslightwhichisthe
s&mulusforvision
• Lightismadeupofpar&clescalledphotonsandit
travelsinwaves
• Thevisiblespectrumoflightisbetweenapproximately
400and700nanometresinwavelength
• Thedifferentwavelengthswithinourvisiblespectrum
appeartousasdifferentcolours
Thepartoftheelectromagne&cspectrumthatourvisual
receptorscandetectisrestrictedtoanarrowrange
Threephysicalcharacteris&csoflightaffectvisualpercep&on
VisualSensa&on
• Threephysicalcharacteris&csoflightaffectthree
psychologicaldimensionsofourvision:
• Hue:referstotheexperienceofcolourbasedonthe
wavelengthoflightthatas&mulusemitsorreflects
• Brightness:referstotheintensityoflightthanan
objectemitsorreflects
• Satura&on:referstothepurityofcolour
• Usingthesethreedimensionswecandiscriminate
betweensevenmilliondifferentcolours(Geldard,1972)
MajorStructuresoftheEye
MajorStructuresoftheEye
• Lightentersthevisualsystemthroughtheeye
• Cornea:atransparentstructurecoveringthefrontoftheeye
• Irissurroundsthepupilanddetermineshowmuchlightgets
tothebackoftheeyebydila&ngorconstric&ngthepupil
• Lens:changesshapetoallowustofocusonobjectsthatare
nearorfaraway
• Lensfocuseslightthatenterstheeyeontonervecellsinthe
backoftheeyecalledthere&na
• Ourabilitytoseeisbasedthetransduc&onoflightinto
electricalimpulsesbythephotoreceptorsinourre&na
Re&nalphotoreceptors(rodsandcones)transducelightinto
neuralimpulsesthatthebraincanprocessasavisualsignal
Re&nalPhotoreceptors
• Re&naiscomprisedtotwokindsofphotoreceptors
• Rodsenableustoseeinpoorlightbecausetheyare
highlysensi&vetolight,butarenotsensi&vetospecific
wavelengthsoflightsodonotenableustoseecolour
• Conesaresensi&vetospecificwavelengthsoflight,so
werelyonthemforcolourvision
• Thefovea,inthecentreoftheeyewherevisionis
sharpest,iscompriseden&relyofcones
• Peripheralre&nacontainssomecones,butmainlyrods
Photoreceptorss&mulatebipolarcells,which
inturncausere&nalganglioncellstofire
Axonsofre&nalganglioncellsformtheop&cnerve
whichexitstheeyethroughtheop&cdisk(blindspot)
TheVisualSystem
VisionintheBrain
• Visualinforma&onleavingthere&natravelsviathe
op&cnervetoneuronsinthesuperiorcolliculus,
whichthencommunicateswiththethalamus
• Fromthethalamus,visualinputtravelstotheprimary
visualcortex(PVC)intheoccipitallobe,whereitis
processedtoenablethedetec&onofsimplefeatures
(Hubel&Weisel,1959)
• Detec&onofcomplexvisuals&mulioccursasaresult
ofcircuitryinvolvingassocia&onareasofvisualcortex
“Where/How”(parietal)cor&calvisualpathway
processesinforma&onaboutthespa&alloca&onofan
objectandhowwecangraspit
“What”(temporal)visualpathwayprocesses
informa&onabouttheiden&tyofanobject
Spa&alneglectresultsfromdamageto
the“where/how”visualpathway
Visualagnosia(e.g.,prosopagnosia)results
fromdamagetothe“what”visualpathway
GestaltPrinciplesofGrouping
• Ourbrainsareorganizedtofillinmissingpartssothatwe
perceiveandrecognizemeaningfuls&muli
• Gestaltpsychology:focusedonunderstandingprinciplesin
whichweperceiveandrecognizevisuals&muliintheiren&rety
despitelimitedinforma&on(Kohler,1929;Wertheimer,1923)
• TheGestaltprinciplesofformpercep&oncharacterizemuchof
ourperceptualorganiza&on(Palmer,1992)
• Theprimaryno&onunderlyingtheGestaltapproachisthelaw
ofPräegnanz:wetendtoperceiveavisualsceneinawaythat
mostsimplyorganizesthedifferentelementsintoastableand
coherentform
Figure-groundsegrega&on:percep&onisorganized
bydis&nguishingbetweenafigureandabackground
Wearebiasedtoperceives&mulithatarelowerina
visualsceneasbeingthefigureratherthantheground
Veceraetal.(2002)
EachGestaltgroupingprincipledemonstratesthe
fundamentallowofPräegnanz,whichstatesthat
throughpercep&onweunifydisparatevisuals&muli
intoacoherentandstablewhole
PerceptualConstancy
• Perceptualconstanciesdescribeourtendencytoview
objectsasunchangingeventhoughtheactualvisual
sensa&onsareconstantlyshiping(Goldstein,2010)
• Colourconstancy:ourpercep&onofcoloursremains
constantasillumina&onchanges
• Sizeconstancy:oncewehavelearnedthesizeofan
objectweassumethatitdoesnotchange
• Shapeconstancy:oncewehavelearnedhowanobject
isshapedweassumethatitdoesnotchange
PerceptualConstancy
• Perceptualconstancieshelpusmakesenseofthe
constantlychanging,perceptuallyconfusingworld
• Perceptualillusionsoccurwhenourassump&ons
aboutperceptualconstanciesareextendedto
situa&onswheretheydon’tapply
TheAmesRoom
Muller-LyerIllusion
Ourexperienceofcolourisshapedbyphysiological
mechanisms,bothinthereceptorsandinopponentneurons
Trichroma&cTheoryofColourVision
• Trichroma&ctheoryappliestothefirstlevelofcolourvision,
whichoccursinthere&na
• Accordingtothistheory,therearethreedifferenttypesof
conesinthere&naandeachtyperespondstoadifferentrange
ofwavelengthsoflight
• Shortwavelengths:givesrisetoexperienceofblue-purple
• Mediumwavelengths:givesrisetoexperienceofgreen
• Longwavelengths:givesrisetoexperienceofred-yellow
• Thethousandsofcoloursthatweseearetheresultofthe
combinedac&vityofthesethreetypesofconephotoreceptors
Threedifferenttypesofconephotoreceptors
respondmaximallytodifferentwavelengthsoflight
Opponent-ProcessTheory
ofColourVision
• Opponent-processtheoryappliestothesecondstageof
colourvision,whichoccursinganglioncellsinthere&naand
inneuronsinthethalamusandvisualcortex
• Theoryassertsthatcoloursexistinpairsthatworktoinhibit
oneanotherwithrespecttocolourpercep&on
• Opponent-processcellsanalyzeinforma&onintermsof
antagonis&copponentcolourpairs:red-green;yellow-blue;
black-white
• Opponent-processingistheresultofac&vityinthethalamus
calledtheLGN-inputstothisnucleusfromonecolourofan
opposingpairinhibitthosefromtheothercolourinthepair
Opponent-ProcessTheory
ofColourVision
• Cellsthatfireinresponsetoapar&cularcolourstop
firingwhenthatcolourisremoved,justastheywould
iftheopposingcolourwerepresent
• Aperimageshappenwhenonecolourinanopponent
pairinhibitstheother
• Whenwereleasethisinhibi&onbylookingawayfrom
thefirstcolour,thepreviouslyinhibitedcolour
overcompensatesandcreatesanimageinthe
opposingcolour
AuditorySensa&on
• Asounds&mulusoccurswhenthemovementsor
vibra&onsofanobjectcausepressurechangesinan
elas&cmedium(e.g.,air,water)surroundingtheobject
• Whenpressurechangespushmoleculestogetherand
increasedensityitiscalledcondensa&on
• Whenpressurechangescausemoleculestospread
out,anddensitytodecrease,itiscalledrarefac&on
S&mulusforsoundisawaveofpressurethatis
createdwhenatransmirngsubstancevibrates
Vibra&onscausemoleculesinthetransmirng
substancetomovetogetherandapart
PhysicalCharacteris&csofSound
• Thephysicalcharacteris&csofthesoundwave
determinehowitisexperiencedpsychologically
• Pitch:thepsychologicaldimensionrelatedtothe
frequencyofthesoundwave(e.g.,1Hz=1cycle/sec)
• Loudness:thepsychologicaldimensionrelatedtothe
intensityofthesoundwave’spressure(i.e.,amplitude)
(measuredindecibels)
StructuresoftheEar
TheOuterEar
• Pinnae:s&cksoutfromthesideofthehead
• Soundwavespassthroughtheouterear,throughthe
earcanaltoanoval-shapedtotympanicmembrane
(i.e.,theeardrum)
• Soundwavescausetheeardrumtovibrate
• Vibra&onsonthetympanicmembranearetransmiQed
tostructuresinmiddleear
Thethreebonesofthemiddleeartransmitthevibra&ons
ofthetympanicmembranetotheinnerear
TheMiddleEar
• Movementoftheossicles(i.e.,threesmallestbonesin
thebody)intensifiestheforceofthevibra&on
• Malleus(hammer)isaQachedtothetympanic
membrane,ittransmitsthevibra&onsthatitreceives
totheincus(anvil)whichsubsequentlytransmitsits
vibra&onstothestapes(s&rrup)
• Thestapesthentransmitsitsvibra&onsignalintothe
innerearbypushingontheovalwindow,amembrane
thatseparatestheossiclesandtheinnerear
TheInnerEar
• Mainstructureoftheinnerearisthecochlea-a
liquid-filled,coiledtubularstructure
• Liquidinsidethecochleavibratesinresponsetothe
movementofthestapesagainsttheovalwindow(i.e.,
theinner-earfluidformsawaveinsidethecochlea
whichdeflectsalongthebasilarmembrane)
• Basilarmembraneiscoveredinrowsofhaircells(or
cilia),whicharetheauditorysensoryreceptors
Haircellsrestonthebasilarmembraneofthecochlea
Vibra&onofthecochlearpar&&oncauses
mo&onofthebasilarmembrane
TheInnerEar
• Movementofthebasilarmembranebendsthehair
cellswhichtransducethe(fluid)soundwaveintoan
electricalsignal
• Haircellscommunicatewiththeauditorynerve,which
sendsthesignaltothebrain
• Signaltravelstothemedialgeniculatenucleus(MGN)
inthethalamus,andisthenrelayedtotheprimary
auditorycortexinthetemporallobe
Iden&fyingFrequencyandPitch
• Frequencytheory:thepercep&onofpitchisrelatedtothefrequencyat
whichthebasilarmembranevibrates
• Differentfrequenciesareconvertedintodifferentratesofac&on
poten&alsinourauditorynerves
• High-frequencysoundscreateshort,fastwavesandlow-frequency
soundscreatelong,slowerwaves
• Placetheory:howweperceivepitchisbasedontheloca&on(place)
alongthebasilarmembranethatsounds&mulates
• High-frequencysoundss&mulatehaircellsnearthebaseofthe
cochleaandlow-frequencysoundss&mulatehaircellsattheendof
thecochlea
• Frequencyisindicatedbytheplacewherenervefiringisthehighest
Tac&leSensa&on
• Skinprovidesinforma&onaboutthes&mulithatwe
comeincontactwith(e.g.,hot,cold,rough,pain)
• Facilitatesinterac&onintheenvironmentbecauseit
preventsusfromgernginjured(e.g.,familial
dysautonomia)andallowsustofeelthepleasurefrom
beingtouched(e.g.,contactcomfort,sex)
• Alsokeepsbodilyfluidscontained,andprevents
harmfulagentsfromenteringthebody(e.g.,dirt,
bacteria,chemicals)
Theskincontainsavarietyofsensoryreceptors
thatregisterdifferenttypesofphysicals&muli
SomatosensoryPathwaystotheCortex
SomatosensoryCortex
Nocicep&vepainreceptorsintheskin
Tac&lePercep&onofPain
• Largeindividualdifferencesinpainthresholdandthe
degreetowhichitcausesemo&onalsuffering
• Peopledifferintheirsensa&onandpercep&onofpain
duetophysicaldifferencesintheirsensorysystems
• Womenhavealowerthresholdfordetec&ngpain
comparedwithmen(Garciaetal.,2007)
• People’sbrainsreactdifferentlydependingonhow
sensi&vetheyaretopain(Dubeetal.,2009)
GateControlTheoryofPain
• PaQernsofneuralac&vitycreatea“gate”preven&ngpain
messagesfromreachingthebrain(Melzack&Wall,1965)
• Ga&ngmechanismdeterminesthestrengthofthepain
signalthatentersthebrainfromthespinalcord
• Ga&ngmechanismstrengthmayexplainindividual
differencesinpainsensi&vity(Romanelli&Esposito,
2004)
• Painpercep&onisdeterminedbyabalancebetween
inputfromphysical(i.e.,nociceptorsintheskin)and
cogni&vefactors(e.g.,expecta&on,aQen&on,distrac&on)
PhantomLimbPain
• Amputeesopenfeelpainfrombodypartthathasbeenremoved
• Neuronsinthebrainthatarerelatedtoourbodilysensa&ons
produceabnormalpaQernsofac&vityandtheresultcanbepain
(Melzack,1992)
• Inaddi&ontorespondingtoincomingpainsignalsthebrainis
alsocapableofgenera&ngpainonitsown
• Phantomsensa&onsaretheresultofabnormalac&vityinthe
somatosensorycortex
• Whenthelimbisremoved,thepartofthesomatosensorycortex
thatpreviouslyreceiveditsinputisinnervatedbyinputsfrom
intactbodyparts(Ramachandran,2005)
(Ramachandran&Rogers-Ramachandran,1996)
TheChemicalSenses
• Smellandtasteinvolveresponsestochemicals,so
togethertheyarecalledthechemicalsenses
• Bothsensesemergedearlyinourevolu&onaryhistory
andtheirvalueisopenunderes&mated(Doty,1986)
• Gatekeepersofthebody:iden&fythingsthatshouldbe
consumed,detectthingsthatwouldbeharmfuland
shouldberejected
OlfactorySensa&on
• Sensa&onintheolfactorysystembeginswhen
chemicalscalledodourantsenterthenose
• Chemicalodourantsaretransducedintoneuralsignals
whentheycomeintocontactwiththeciliaofolfactory
sensoryreceptorneuronslocatedinthenasalmucosa
• Whenodourantsenterthenosetheybindtoreceptors
locatedonolfactorysensoryreceptorneurons
• Anac&onpoten&aloccursinolfactorysensory
receptorneuronswhenenoughodourantmolecules
bindtoreceptors
Olfactoryreceptorneuronstransduceinforma&on
fromodourantmoleculesthatenterthenose
Thisinforma&oniscarriedbytheolfactorynerveinto
thebrainwhereitsynapsesintheolfactorybulb
OlfactorySensa&on
• Ourthresholdsfordetec&ngodourshaveawide
distribu&on:somewecandetecteasily,butnotaswell
• Ourabilitytodetectodoursismuchpoorerthanmany
otheranimals(e.g.,dogsare300-10,000&mesmore
sensi&ve)
• Differencesinsensi&vityarenotcausedbythe
sensi&vityofsensoryreceptors,ratheritisbecausewe
havefarfewerreceptorsthanmacrosma&canimals
• Althoughwedohavegooddetec&onthresholdsfor
someodours,ourrecogni&onthresholdsarequitepoor
OlfactoryPercep&on
• Signalsfromourolfactoryreceptorneuronstravelto
thebrainthroughtheolfactorynerve
• Firstthisinforma&ontravelstotheolfactorybulbat
thebaseofthebrainbeneaththefrontallobes
• Olfactoryinforma&onthensenttocor&calregions
involvedinrecognizinganddiscrimina&ngodours
• TheabilityofourcortextorecognizepaQernsofinputs
fromavarietyofolfactoryreceptorsisprobablyhow
weareabletodetectcertainodours
OlfactoryPercep&on
• Theolfactorybulbprojectstotheamygdala,aswellas
indirectlytothehippocampus,anareaimportantfor
learningandmemory
• Abilityofsmellstoelicitmemoriesisprobablyrelated
toolfactoryconnec&onstothehippocampusand
amygdala(Lehrer,2007)
Flavourisdeterminedbytasteandodour:withoutsmell
itisdifficulttoiden&fythetasteoffoodonthetongue
Gustatory(Taste)Sensa&on
• Flavourisacombina&onofsmellandtaste
• Tasteoccursbecausechemicalss&mulatesensoryreceptorsonthe
tongue,whichare&nybumpsarecalledpapillae
• Tonguecontainsfourdifferenttypesofpapillae:filiform,fungiform,
foliate,circumvilliate
• Papillaearelinedwithtastebuds,whicharelikenestsoftastereceptor
cells,eachcontaining60-100sensoryreceptorcells
• Tastereceptorcellshaveciliathatcontainthesensoryreceptors,these
ciliaextendthroughtheporesofthetastereceptorandareexposedto
whatisinourmouth
• Eachofthefivemajortastereceptorsrespondstospecifictastein
food:sweet,sour,biQer,salty,umami
Thereare9,000tastebudsinhumangustatorysystem
Receptorcellsfortasteareclusteredwithinthetaste
budsfoundinthepapillae(bumps)thatcoverthetongue
Gustatory(Taste)Percep&on
• Tasteinforma&onisintegratedwithrewardcircuitsin
thebrain(Norgrenetal.,2006)
• Informa&onabouttasteandsmellisprocessedin
separatepathwaysthatconvergeintheprefrontal
cortex(PFC)
• Insulaisac&vatedwhenwetaste,smell,orevensee
somethingthatisdisgus&ng(Calderetal.,2007)
IndividualDifferencesinSmellandTaste
• Femalesaremoresensi&vetosmellthanmales,and
theirsensi&vityvarieswiththemenstrualcycle(Derntl
etal.,2013)
• Higherpropor&onof“super-tasters”arefemales(i.e.,
sensi&vetoaspecificbiQersubstance)
• Heightenedsensi&vityofbothchemicalsensesin
femaleslikelyhasadap&vesignificance